Method and device for the production of a workpiece with internal toothing, in particular a hollow wheel

ABSTRACT

The invention relates to a method and an apparatus for producing a workpiece with internal toothing, especially an internal geared wheel, by using a cup shaped preform (N) with a substantially cylindrical side wall (N 1 ) and a mandrel ( 5 ) with an external profile ( 6 ) according to the internal toothing to be produced, as well as with a forming tool which reduces the outside diameter of the cylindrical side wall during an advancing movement, as a result of which the material of the cylinder wall region flows into the external profile ( 6 ) of the mandrel ( 5 ). In accordance with the invention, the forming tool is configured as a drawing ring ( 14 ) ensuring the ironing of the cylinder wall region (N 1 ) during an advancing movement and that two tool elements act upon the preform (N) during the ironing, which tool elements produce axial compressive stresses in the cylinder wall region (N 1 ) of the preform.

BACKGROUND OF THE INVENTION

The invention relates to a method and an apparatus for producing aworkpiece with internal toothing, especially an internal geared wheel,according to an apparatus for producing a workpiece with internaltoothing, especially an internal geared wheel. Such internal toothingsare produced by means of flow turning. A cup-like preform is pressedaccording to DE 198 30 817 A1 by means of tapered rollers during anadvancing movement against a clamping chuck which has the externalprofile of the internal toothing to be produced. Said preform is reducedin its diameter, with the preform rotating relative to the taperedrollers. The material of the cylinder wall region of the preform flowsinto the profile of the clamping chuck, as a result of which the innerprofile of the workpiece is produced. The disadvantageous aspect is thehigh amount of flexing work which stresses the workpiece material duringthe flow turning and the thus inadequate quality of the producedinternal toothing. A high local introduction of energy is connected withthe flexing work which leads to energy losses. The external toothing aspictured therein frequently breaks off as a result of the high stresseson the clamping chuck. Moreover, the productivity of this method isrelatively low despite a high need for machinery because only three tofour parts per minute can be produced.

BRIEF SUMMARY OF THE INVENTION

It is the object of the present invention to provide a method and anapparatus for an energy-saving production of a workpiece with internaltoothing, especially an internal geared wheel, which ensures asubstantial increase in the productivity at high quality of the internaltoothing with a relatively simple constructional configuration of theapparatus.

This object is achieved by the features of an apparatus for producing aworkpiece with internal toothing, especially an internal geared wheelfor a gearing, comprises a mandrel with an outside profile according tothe internal toothing to be produced as well as a forming tool whichreduces during an advancing movement the outside diameter of a cup-likepreform, as a result of which material of the cylinder wall region flowsinto the outside profile of the mandrel. In accordance with theinvention, a drawing ring is used as the forming tool which ensuresironing of the cylinder wall region during an advancing movement.

In the direction towards the lower side of the floor of the preform anaxially movable counterholder is arranged in such a way that during theironing it acts with a counterholding force on the lower side of thefloor of the preform. The counterholder may comprise a circular pressuresurface facing in the direction towards the lower side of the floor,which pressure surface substantially acts upon the entire floor region,or said counterholder may comprise a ring-like pressure surface which isadjusted to the width of the cylinder wall of the preform and is alignedessentially flush with the same and acts upon the edge region of thelower side of the floor of the preform.

An axially movable pressure punch is arranged in the direction towardsthe face surface of the cylindrical side wall in such a way that duringthe ironing it acts upon the face surface with a pressure force. Thepressure punch can be moved during the ironing by a movementcorresponding to the ironing length of the preform in the direction ofthe advancing movement of the drawing ring.

Advantageously, the axial stroke movement of the pressure punch asoccurs during the ironing can be controlled depending on its pressureforce. For this purpose the pressure punch is held in an axially movablefashion by means of a hydraulic piston.

The apparatus can advantageously be integrated in a hydraulic pressconsisting of a bedplate and a press ram. The mandrel is arranged in anaxially fixed fashion on the bedplate and the press stamp is held on themandrel in a manner so as to be axially displaceable by means of ahydraulic piston. The drawing ring is arranged on the press stamp in apreferably fixed manner and the counterholder is arranged thereonpreferably in an axially movable fashion by means of a hydraulic piston.The pressure punch is preferably arranged as a cylindrical pressuresleeve. The distance of the pressure surface which is adjusted to thelength of the preform to the face side of the mandrel can be adjusted bymeans of spacer rings for example.

For ejecting the workpiece the mandrel is held in a rotatable manner inthe production of a helical gearing.

With respect to the method employed, the production of the workpiecewith internal toothing occurs in such a way that a cup-like preform,comprising a floor and substantially cylindrical side walls, is reducedin its outside diameter by means of a mandrel having the externalprofile according to the internal toothing to be produced, so that thematerial of the cylinder wall region flows into the external profile ofthe mandrel. According to the invention, the reduction of the outsidediameter occurs by ironing by means of a drawing ring. During theironing the axial compressive stresses are applied onto the cylindricalside walls of the preform, so that the flow of material into the profileof the mandrel is promoted. The axial compressive stresses arepreferably applied by a pressure punch acting upon the face side of thecylinder wall. A counterholder acts simultaneously on the lower side ofthe floor in order to avoid deformations in the floor region and toapply a counterholding force. The counterholding force of thecounterholder and the force of the pressure punch should be controllablewith respect to each other in such a way that during the entire ironingprocess a flow of material is ensured in the radial direction tocompletely fill the shape of the mandrel.

During the ironing, the pressure punch carries out an axial strokemovement according to the ironing length of the preform in the directionof the advancing movement of the drawing ring which is controlleddepending on its pressure force.

The invention allows for the first time producing internally gearedworkpieces in high quality on a conventional press in an energy-savingmanner. The productivity can be increased by four to six times incomparison with flow-turning.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is now explained in closer detail by reference to anembodiment and the pertinent drawings, wherein:

FIG. 1 shows an apparatus with an inserted preform before the ironing;

FIG. 2 shows an apparatus during the ironing;

FIG. 3 shows an apparatus with an inserted preform and material overflowin the counterholder before the ironing;

FIG. 4 shows an apparatus according to FIG. 3 during the ironing;

FIG. 5 shows an apparatus after ending the ironing with an additionalcalibrating pressure and additional material overflow at the end of thecylindrical edge of the workpiece.

DETAILED DESCRIPTION OF THE INVENTION

FIGS. 1 and 2 show the principal configuration of the apparatus asintegrated in a press. The lower part 2 of the tool is arranged on thebedplate 1, which lower part comprises a first hydraulic piston 3. Themandrel 5 is fastened in an axially fixed manner via a stamp 4 to thelower part 2 of the tool, which mandrel has an external profile 6. Anejector 7 extends in the middle of the stamp 4 and the mandrel 5. Thepressure punch 9 which is arranged as a pressure sleeve is held in anaxially movable way on the hydraulic piston 3 via an adapter 8. Theaxial position of the pressure punch 9 can be changed via spacers 10which can be attached between the adapter 8 and the pressure punch 9.The upper part 11 of the tool is arranged on the press ram P andcomprises a counterholder 12 which is axially adjustable via a secondhydraulic piston 13. The drawing ring 14 is fastened in a fixed manneron the press ram via an adapter 15.

According to FIG. 1 the cup-like preform N was placed over mandrel 5with the cylindrical edge N1 facing downwardly, so that the face surfaceN2 faces in the direction towards the press stamp 9 and the lower sideof floor N3 faces in the direction towards the counterholder 12.According to the method, the hydraulic piston 13 moves the counterholder12 in the direction towards the lower part of the tool until thecounterholder 12 rests on the lower side of floor N3.

The drawing ring 14 which is arranged in a fixed fashion on the pressram P moves in the pre-stroke with the press ram P in the directiontowards the bedplate 1. At the same time, the first hydraulic piston 3is pressurized and presses the press stamp 9 with the force F1 againstthe face surface N2 of the preform N (FIG. 2). At the same time, thecounterholder 12 acts a counterholding force F2 on the floor of the cup.During the ironing the pressure punch 9 performs a movement in thedirection of the pre-stroke of the drawing ring 14 according to thedrawing of the preform N, with the pressure acting upon the wall N2being maintained by the forces F1 and F2. As a result of the compressivestresses produced in the workpiece wall N2, the flow of material ispromoted, so that the material flows reliably into the profile 6 of themandrel 5. An outstanding quality of the internal toothing is thusachieved. After the completion of the ironing, the upper part 11 of thetool moves upwardly and the workpiece is removed form the mandrel 5 bymeans of the ejector 7, with the same being held in a rotatable fashionin the case of a helical gearing.

In order to allow excessive material to flow off and to avoidoverloading the tool it is possible according to FIGS. 3 and 4 toprovide a material overflow 12.2 in the counterholder 12. Thecounterholder 12 comprises a thrust member 12.1 in the direction towardsthe workpiece N, which member is also reduced in its diameter in thedirection towards the workpiece N, thus producing a gap between thethrust member 12.1 and adapter 15 into which the excessive material canflow and which is thus used as a material overflow 12.2.

According to FIG. 5 it is also possible, in addition to the materialoverflow 12.2 as provided for in FIGS. 3 and 4, to arrange a furthermaterial overflow 12.3 at the end of the cylindrical wall. The gapbetween the outside diameter of the pressure punch 9 and the innerdiameter of the drawing ring 14 can be used for this purpose.

It is further advantageous when at the end of the forming process anincreased axial pressure for calibration is exerted in order to achievea better filling and a higher excessive material can flow off asdescribed above. After cylinder 3.1 is situated in its lowermostposition. The increased pressure can now be applied in such a way forexample that the pressure punch 9 via an intermediate piece Z whichcomprises a thread G on its outside diameter and is connected above witha ring follower G1 which on its part rest on the cylinder 3.1 and thuson the bedplate 1 via the lower part 2 of the tool.

1. An apparatus for producing a workpiece with internal teeth from acup-shaped preform having a substantially cylindrical side wall and acup base at one axial end of said sidewall, said apparatus comprising: apress bed plate; a mandrel axially fixedly mounted on said bed plate,said mandrel having an external profile corresponding to the internalteeth to be produced on the workpiece; an annular punch surrounding saidmandrel, said punch being moveable axially relative to said mandrel sothat the punch can engage an axial end face of a preform disposed onsaid mandrel with an inside surface of said cup base contacting saidmandrel; a press ram movable to advance toward said base plate; aforming tool in the form of a drawing ring axially fixedly mounted onsaid press ram, said drawing ring surrounding said punch and having anarea of reduced inner diameter for reducing the diameter of thecylindrical sidewall of the preform on the mandrel during an advancingmovement of the press ram and drawing ring and causing material of thecylindrical side wall to flow into the external profile of the mandrel;and a counter holder mounted on said press ram; said counter holderbeing moveable axially relative to said drawing ring so that the counterholder can engage an outside surface of said cup base of the preform onthe mandrel; wherein said annular punch and said counter holder exertopposing axial forces on the preform to produce compressive stress inthe cylindrical sidewall of the preform during the advancing movement ofthe press ram and drawing ring.
 2. An apparatus according to claim 1,further comprising an ejector in said mandrel for ejecting an internallytoothed workpiece from the mandrel when the apparatus is opened.
 3. Anapparatus according to claim 1, wherein said counter holder comprises acircular pressure surface facing the outside surface of the cup base ofthe preform, said circular pressure surface acting upon substantiallythe entire base of the preform.
 4. An apparatus according to claim 1,wherein said counter member comprises an annular pressure surface whichis aligned with the cylindrical wall of the preform, said annularpressure surface acting upon a radially outer annular region of the baseof the preform.
 5. An apparatus according to claim 1, wherein saidpressure punch is moveable axially by a hydraulic piston.
 6. Anapparatus according to claim 1, wherein said counter holder is moveableaxially by a hydraulic piston.
 7. An apparatus according to claim 1,wherein a gap is provided between the counter holder and a tool part onthe press ram into which material overflow from the preform can flow. 8.An apparatus according to claim 1, wherein a gap is provided between theannular punch and the drawing ring into which material overflow from thepreform can flow.
 9. An apparatus according to claim 1, wherein saidmandrel is rotatably mounted for ejecting the workpiece.
 10. Anapparatus according to claim 1, wherein said drawing ring comprises aninner cylindrical section having an inner diameter just larger than theouter diameter of the preform, a first frustoconical section whichconverges from said inner cylindrical section to said area of reducedinner diameter, and a second frustroconical section on the other side ofthe reduced diameter area which diverges from said reduced diameter areato a larger diameter than said reduced diameter area.
 11. A method ofproducing a workpiece with internal teeth, said method comprising:providing a cup-shaped preform having a substantially cylindricalsidewall and a cup base at one axial end of the sidewall; disposing thepreform in a forming tool with the inside surface of the cup basecontacting a mandrel fixedly mounted on a press bed plate, said mandrelhaving an external profile corresponding to the internal teeth to beproduced on the workpiece; contacting an end face at a second axial endof the preform with an annular punch surrounding said mandrel; saidannular punch being moveable axially relative to said mandrel and pressbed plate; contacting the outside surface of the cup base with a counterholder mounted on a press ram moveable to advance toward said bed plate;said counter holder being moveable axially relative to said press ram;providing a forming tool in the form of a drawing ring fixedly mountedon the press ram, said drawing ring surrounding said punch and having anarea of reduced inner diameter smaller than the outer diameter of thecylindrical sidewall of the preform, and advancing the press ram to movethe reduced diameter area of the drawing ring along the exterior of thecylindrical sidewall of the preform to reduce the diameter of thecylindrical sidewall and cause material of the cylindrical side wall toflow into the external profile of the mandrel; said annular punch andsaid counter holder exerting opposing axial forces on the preform toproduce compressive stress in the cylindrical sidewall of the preformduring the advancing movement of the press ram and drawing ring.
 12. Amethod according to claim 11, wherein said preform is elongated duringthe advancing movement of the drawing ring, and wherein the annularpunch retracts toward the bed plate an amount equal to the elongation ofthe preform.
 13. A method according to claim 11, wherein said drawingring comprises an inner cylindrical section having an inner diameterjust larger than the outer diameter of the preform, a firstfrustoconical section which converges from said inner cylindricalsection to said area of reduced inner diameter, and a secondfrustroconical section on the other side of the reduced diameter areawhich diverges from said reduced diameter area to a larger diameter thansaid reduced diameter area.
 14. A method according to claim 11, whereinupon completion of the advancing movement of the press ram, an increasedaxial force is exerted on the formed workpiece for calibrating theworkpiece.
 15. A method according to claim 11, wherein during productionof the workpiece, excess material from the workpiece flows into amaterial overflow gap.
 16. A method according to claim 15, wherein saidmaterial overflow gap is between the counter holder and a tool partmounted on the press ram.
 17. A method according to claim 15, whereinsaid material overflow gap is between the annular punch and the drawingring.
 18. A method according to claim 11, further comprising retractingthe press ram to open the tool, and rotating said mandrel to eject theformed workpiece.
 19. A method according to claim 11, wherein saidpressure punch is moved axially by a hydraulic piston.
 20. A methodaccording to claim 11, wherein said counter holder is moved axially by ahydraulic piston.